This article proposes a novel maintenance scheduling optimization model for a transmission company, the model corresponds to a mixed integer linear programming (MILP) problem. The main contribution of the model is the inclusion in the objective function of incentives for minimizing the equipment unavailability that results from the maintenance activities. Another contribution of the model is that it avoids simultaneous disconnection of equipment which generates insecure conditions for the operation of the network or unnecessary interruptions of electricity. Finally, an example application to the Peruvian system is presented and it was found that the model obtains 12% less interruptions with respect to executed maintenance.